Objective:

To monitor the formation of an imine by NMR using piperonal and 5-methylfurfurylamine.

Procedure:

In separate 1 dram vials was added 5-methylfurfurylamine (111uL, 1mmol) and piperonal (0.150g, 1mmol) and then diluted to 1mL with CDCl3. A NMR spectra was taken for each. To a separate vial each solution was added and shaken vigorously. A NMR spectra was taken at different time intervalsl to monitor the progression of the reaction.

Results:

NMR

Starting materials

40A (HMR piperonal) (methylene dioxy protons at 6.0,aromatic protons at 6.8, & 7.3 ppm, aldehyde proton at 9.7ppm, residual acetone? at 2.0ppm)
40B (CMR piperonal) (aldehyde peak at 190, quaternary carbons at 132ppm, 149ppm & 153 ppm, aromatic carbons at 138, 109 & 107ppm, methylene dioxy carbon at 102ppm)
40C (HMR 5-methylfurfurylamine) (methyl group at 2.1, methylene group at 3.6ppm, furan protons at 5.7, 5.9ppm. There is some problem with integration with this spectra)
40D (CMR 5-methylfurfurylamine) (quaternary carbons at 150 and 154 ppm, carbons on ring at 106 ppm, methylene group at 39ppm, and methyl group at 16ppm)

5 mins

40E (HNMR) (27.1% conversion of 9.7 to 8.2 ppm)

10 mins

40F(HNMR)

20 mins

40G 42.5% conversion

25 mins

40Q(CMR)

40 mins

40H (HMR) 59.8 % conversion

100 mins

40I (HNMR) 71.4% conversion

105 mins

40J (CMR)

180 mins

40K(HNMR) 78.9% conversion

265 mins

40L(CMR)

465 mins

40N(HNMR) 83.8% conversion
40M(CMR)

22hr 15 mins

40P(HNMR) 90.1% conversion
40O(CMR)

Other Data

Data for imine formation

Discussion

We were able to attribute the imine proton at 8.2 ppm, consistent with other aromatic imines (e.g. 8.5 ppm from Habbibi, 2006). This peak gradually increases in area as the aldehyde proton peak at 9.7 gradually disappears. These two peaks were used to monitor the formation of the imine in this reaction. The reaction goes to 50% after about 30 min and 90% completion after 24 hrs. This is probably an equilibrium since the conversion no longer follows second order kinetics after about 3 h.

Conclusion

The imine formation seems fairly clean between piperonal and 5-methylfurfurylamine in CDCl3. At 0.5M, an equilibrium formed after 22 h favoring the imine to an extent of about 90%. The conversion was 50% complete after about 30 minutes. For future Ugi experiments it may be important to allow the imine to form before adding any other Ugi components.

References

Habbibi, M., Montazerozohori , M., et al "Synthesis, Structural and Spectroscopic Properties a New Schiff Base Ligand N, N' Bis (Trifluoromethylbenzylidene) ethylenediamine" J. Fluorine Chem. Vol. 127, Issue 6, pp 769-73

Knight, P., O'Shaughnessy, P., et al "Biaryl-bridges Schiff Base Complexes of Zirconium Alkyls: Syntheesis, Structure and Stability"
J. of Organometallic Chemistry Vol 683, Issue 1 pp 103-113

Log:

2006-11-07

12:45 Prepared solutions of each component.

2006-11-09

10:30 Took HNMR (40A) and CMR (40B) of piperonal. Took HNMR (40C) and CMR (40D) of 5-methylfurfurylamine.
11:45 Combined each solution in a separate one dram vial shook vigorously for approximately 1 minute.
11:50 Took HNMR (40E, T=5min)
11:55 Took HNMR (40F, T=10min)
12:05 Took HNMR (40G, T= 20min)
12:10 Took CMR (40Q, T=25min)
12:35 Took HNMR (40H, T=40 min)
13:35 Took HNMR (40I, T= 100min), CMR (40J, T=105min)
14:55 Took HNMR (40K, T=180 min)
16:10 Took CMR (40L, T= 265min)
19:30 Took HNMR (40N, T=465min), CMR (40M, T=465 min)

2006-11-10

10:00 Took HNMR (40P, T=22hr, 15min), CMR (40O, T=22hr, 15 min)

Exp040